The American Eclipse Expedition 



593 



two different pieces of glass, as in that 

 case either the red or blue rays must be 

 left outstanding, the red in the photo- 

 graphic objective and the blue in the 

 visual one. This lens is composed of glass 

 manufactured by Mantois & Cie, of 

 France near Paris. The curves were 

 computed by Dr C. S. Hastings, of the 

 Yale University, and the lens constructed 

 by the John A. Brashear Co., of Alle- 

 gheny, Pennsylvania. The most impor- 

 tant part of this instrument, as in all 

 cameras, is the lens, and this lens alone 

 cost $1,000. The camera is actuated 

 from within the house by a focal plane 

 slit and shutter affording an exposure of 

 less than a thousandth of a second when 

 used in full sunlight, but of course during 

 the eclipse the exposures were much 

 longer. 



The illustration shown is the 65- 

 foot photoheliograph, on which a vast 

 amount of thought was expended. It is 

 composed of a long wooden framework 

 ending in a little house. The house is 

 made to be taken apart for transporta- 

 tion, and contains a double door, so that 

 members of the party may enter it without 

 admitting light. Portions of the roof are 

 hinged to allow ventilation and light 

 when desired. The photoheliograph is 

 set up on a horizontal plane, and the 

 light from the sun is reflected into the 

 long box or camera through the lens 

 by means of a ccelostat. The ccelostat is 

 simply a mirror or set of mirrors on a 

 movable polar axis which is actuated by 

 clock-work regulated for solar time, by 

 which the reflected image of the sun, 

 which has apparent motion, is always 

 maintained in the line of collimation of 

 the camera. This instrument is some- 

 times called Joshua because it makes the 

 sun stand still. Formerly such cameras 

 were set up pointing directly at the sun, 

 the upper end resting upon a scaffold ; 

 but while this installation has some ad- 

 vantages, so long an instrument thus 

 mounted is more or less unstable, and the 

 difficulties of protecting it from the wind 

 and in making the adjustments are 

 greatly augmented. 



Three new polar axes were con- 

 structed, one for each of the three prin- 

 cipal observing stations. These were 

 made of iron, which gave a much more 

 rigid support to the delicate photographic 

 cameras and telescopes that were at- 

 tached to them than was possible with the 

 old wooden machines heretofore relied 

 upon for the purpose. The axes carry- 

 ing the cameras and other instruments 

 were set up on wooden frames and ad- 

 justed parallel to the axis of the earth; 

 hence its name polar axis. The whole 

 apparatus was made to take apart for 

 transportation, and as thus constructed 

 the same instruments could be used many 

 times over. 



The polar axes were strong enough to 

 carry photographic cameras, some of 

 which were also made of angle-irons 10 

 to 15 feet in length. Ccelostats were also 

 used to reflect the image of the sun into 

 other instruments, such as the spectro- 

 scopes. 



The instruments, having all been set 

 up and adjusted, were taken apart, 

 boxed, and transported to Alexandria, 

 Virginia, where they were shipped on 

 board the Ccesar for ports in the Medi- 

 terranean. 



crossing the; ocean 



The vessels assigned for the Special 

 Service Squadron for the purpose of car- 

 rying the experts and furnishing the men 

 who were to assist them in observing the 

 eclipse were the U. S. S. Minneapolis, 

 Captain J. M. Miller, U. S. N., command- 

 ing (which vessel was the flagship of the 

 commander-in-chief) ; the U. S. S. Dixie, 

 Commander G. A. Merriam, U. S. N., 

 commanding ; and the U. S. collier Ccesar, 

 Lieutenant Commander G. H. Stafford, 

 U. S. N., commanding. 



The Ccesar left Alexandria on June 18 

 and Norfolk on June 22 for Gibraltar, 

 and the Dixie left Philadelphia June 26, 

 1905. 



Incidental to but connected with the 

 eclipse problem, is the important study of 

 meteorology. Prof. F. H. Bigelow, of 

 the Weather Bureau, was invited to go 



